Why Is My Period Late?

While pregnancy might be the first thing that comes to mind when your period is late, it isn't the only reason menstruation might be delayed. There are many factors that may contribute to the disruption of a woman's menstrual cycle.

The menstrual cycle is regulated by the endocrine system, which releases hormones — including the sex hormones estrogen and progesterone — into the body. These hormones play a key role in all stages of the menstrual cycle, allowing the ovum (egg) to mature and eventually be released into the uterus.

But many different disorders can result in hormonal imbalances and delayed menstruation, including hypothyroidism (underactive thyroid gland), hyperthyroidism (overactive thyroid gland), pituitary adenoma (noncancerous tumor of the pituitary gland) and adrenal insufficiency (a condition in which the adrenal glands do not produce adequate amounts of certain hormones).

Emotional or physical stress can also delay ovulation and, therefore, menstruation. Severe stress causes a decrease in the amount of gonadotropin-releasing hormone (GnRH) produced by the body. The right amount of GnRH — which controls the release of hormones such as follicle-stimulating hormone (FSH) and estrogen — is needed for ovulation. Stress in the weeks leading up to ovulation, therefore, can be responsible for your late period.

Women who participate in physically intense athletic activities may experience delays in their menstrual cycle, or they may not get their period at all — a condition known as amenorrhea. Experts have several theories for why extreme physical activity disrupts the menstrual cycle, ranging from a low percentage of body fat to poor nutrition and rapid weight loss.

These same theories may help to explain why certain medical conditions — like anorexia, obesity and polycystic ovary syndrome (PCOS) — can lead to late periods.

Certain medicines or medical treatments, including chemotherapy and radiation, can also delay menstruation. And some drugs — including barbiturates (sedatives), corticosteroids, oral contraceptives (birth control pills) and certain tranquilizers — have also been found to disrupt the menstrual cycle.

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Elizabeth Palermo

Elizabeth is a Live Science staff writer who writes about science and technology. She graduated with a B.A. from the George Washington University. Elizabeth has traveled throughout the Americas, studying political systems and indigenous cultures and teaching English to students of all ages.